1. Field of the Invention
The present invention relates to a semiconductor sensor device and, particularly, to a semiconductor sensor device which is realized in the form of a compact chip capable of being electrically trimmed.
2. Description of the Related Art
In a semiconductor pressure sensor and the like, a resistance film is trimmed to a predetermined shape by laser trimming at the time of fabricating the chip in order that the resistance film will roughly acquire a predetermined resistance.
Then, after the sensor chip is mounted in a housing, in many cases, a final trimming adjustment is effected while applying pressure. In the case of a pressure sensor for high-pressure applications, however, it is difficult to effect the laser trimming since the semiconductor chip is hermetically sealed in the housing, and it becomes necessary to effect the trimming electrically.
The electrical trimming is usually carried out by using a fuse memory or an EPROM. However, this requires a number of control terminals (pins) for writing and reading trimming data. Even when the trimming circuit is formed in the same chip as the sensor circuit, the production cost is not decreased but is rather increased due to an increase in the number of pins needed for the chip.
In a pressure sensor for high-pressure applications as shown in FIG. 5, in particular, a sensor chip is disposed in a space 4a at the end of a lower half 41 of the housing, the housing being threaded along its outer circumference 44 for mounting, and lead pins 43 are provided from the terminals of the sensor chip to a space 4b at the upper end of the housing running through an intermediate portion 42 of the housing which has a large thickness to withstand pressure. However, the lead pins which are provided with hermetic sealing 45 are very expensive to produce. This is because the holes through which the lead pins 43 run must be made as small as possible in order to decrease the areas that receive high pressures. This, however, requires a greatly increased period of time for machining and causes the yield to be decreased.
When a pressure sensor having many pins is being used (as a sensor), furthermore, the pins that were provided for trimming and that are now not necessary remain open and are buried in the casing or the housing. However, high-frequency noise (EMI noise) can infiltrate into the sensor circuit through such unnecessary pins and deteriorate the S/N ratio. Moreover, a number of connections such as wire bonds provided between the pins and the sensor chip are detrimental to maintaining reliability.